Non-pollutional process for producing aromatic nitro compounds without using a mineral acid

ABSTRACT

The present invention relates to a process for producing an aromatic nitro compound by introducing a nitrogen oxide gas and ozone-containing oxygen or air into a halogenated organic solvent dissolving or suspending therein an aromatic compound, thereby subjecting the aromatic compound to nitration. By the use of a system comprising the nitrogen oxide and ozone-containing oxygen or air as the nitrating agent, the aromatic nitro compound can be produced under mild conditions without using any mineral acid. In addition, the various disadvantages due to the use of mineral acid in the conventional process can be avoided by the process of the present invention.

DESCRIPTION

1. Technical Field

The present invention relates to a process for producing aromatic nitrocompounds. More particularly, the invention relates to a process forproducing aromatic nitro compounds without using nitric acid or a nitricacid derivative as a direct nitrating agent.

2. Background Art

An aromatic nitro compound is an essential substance as the startingmaterial for the production of a wide variety of typical organicindustrial products such as pharmaceuticals, agricultural chemicals,plastics and explosives. For the industrial synthesis of thesecompounds, ever since the last century, there has been employed a methodin which nitric acid is used either singly or in combination with otheracid catalyst (sulfuric acid, phosphoric acid, etc.) as nitrating agent.

In this method, however, since a large amount of a highly concentratedacid is used, there are always involved the technical problems to besolved, which vary in nature according to the aromatic substrate to benitrated, due to the disadvantage in nitration using nitric acid. Suchproblems include an exothermic reaction under the heterogeneousconditions in addition to danger in operation, treatment of a largeamount of waste acid, use of a corrosion-resistant apparatus,difficulties in achieving continuous automation, tremendous heatgeneration and oxidation of the substrate.

Generally, the nitration reactions of aromatic compounds proceed withthe nitronium ions (NO₂ ⁺) as the reaction species which is generated inthe course of the reaction shown by the following formula, so the singleuse of nitric acid can not provide a satisfactory nitration and it istherefore necessary to combinedly use a strong acid as auxiliary agentfor converting nitric acid into acidinium ion (H₂ NO₃ ⁺):

    HNO.sub.3 +H.sup.+ →(H.sub.2 NO.sub.3.sup.+)→H.sub.2 O+NO.sub.2.sup.+

Concentrated sulfuric acid or fuming sulfuric acid is industrially usedfor this purpose, but great cost is required for recovery or treatmentof the acid after completion of nitration, and also a large amount ofwater or an alkaline agent is necessitated for neutralization andwashing of the product. Furthermore, since the reaction is carried outunder a strongly acidic condition, side reactions involving thecarbocation species or radical cation species generated competitively inthe course of the reaction are unavoidable. Intermixing of the variouswater- or oil-soluble organic compounds produced through the sidereactions into waste water is a serious problem that could not beoverlooked from the standpoint of environmental pollution.

It has been desired to establish a process for effectively producingaromatic nitro compounds without using any inorganic acid, which istroublesome to handle, such as nitric acid, sulfuric acid, phosphoricacid, etc., and with minimized environmental pollution.

DISCLOSURE OF INVENTION

The present inventors have found that the nitrogen oxides, mosttypically nitrogen dioxide, exhibit a strong nitrating function in thepresence of ozone. That is, the present inventors have found that anaromatic compound can be directly nitrated by introducing a gaseousnitrogen oxide and ozone-containing (ozonized) oxygen or air into achemically stable organic solvent having been dissolved or suspendedtherein the aromatic compound and making the nitrogen oxide act to thearomatic compound, under a mild condition at a temperature around roomtemperature. The present invention was attained on the basis of thisfinding.

Thus, the present invention provides:

(1) a process for producing an aromatic nitro compound which comprisesdissolving or suspending an aromatic compound in a halogenated organicsolvent, and introducing into the resulting solution or suspension anitrogen oxide and ozone-containing oxygen or air, thereby nitrating thearomatic compound; and

(2) a process set forth in (1) wherein the nitration is carried out inthe presence of a solid phase carrier, a cation exchange resin or aLewis acid.

The present invention will be described in detail below.

According to the process of the present invention, it is possible toeffectuate not only mononitration but also polynitration such asdinitration and trinitration as desired by properly selecting thereaction conditions. The position substituted by the nitro group(orientation) is, as in the case of using nitric acid as nitratingagent, dependent on the rule in electrophilic reactions. That is, anaromatic compound having an electron donative group represented by alkylgroup shows ortho- or para-orientation and an aromatic compound havingan electron attractive group represented by nitro group showsmeta-orientation, but in both cases the extent of the orientation isslightly weaker than in case of using nitric acid as nitrating agent.

Examples of the aromatic compounds which can be used as the startingmaterial in the process of the present invention include benzene,toluene, (o-, m- or p-)xylene and their mononitro and dinitro compounds;benzenes substituted by one or more of alkyl groups having one or moreof carbon atoms, and their mononitro and dinitro compounds; halogenatedbenzenes such as monochlorobenzene, dichlorobenzene, trichlorobenzene,etc., and their mononitro and dinitro compounds; benzenes substituted byalkyl group and halogen, and their mononitro and dinitro compounds;benzenes substituted by alkoxy group and their mononitro and dinitrocompounds; naphthalene and its derivatives; anthracene and itsderivatives; anthraquinone and its derivatives; pyrene and itsderivatives; and acetanilide derivatives which is optionally substitutedwith alkyl group, alkoxy group or halogen.

The halogenated organic solvent used as solvent in the process of thepresent invention needs to be stable to the nitrogen oxide used as thereacting agent. A halogenated aliphatic compounds are preferably used,and dichloromethane and tetrachloromethane can be mentioned as preferredexamples of such halogenated aliphatic compounds. Two or more of thesolvents may be used in admixture. The amount of the solvent used isusually 2 to 200 times, preferably 5 to 100 times (by weight) the amountof the aromatic compound used as starting material (reaction substrate).Nitrogen tetraoxide, nitrogen dioxide or the like is used as thenitrogen oxide. Such nitrogen oxides may be used in admixture. The gasof such nitrogen oxide can be produced, for example, by oxidizing amixed gas of air and ammonia at a temperature of, for example, 500°to700° C. in the presence of a catalyst (such as platinum,platinum/rhodium or the like).

Ozone-containing oxygen or air can be obtained by, for example, passingoxygen or air through a silent discharge tube.

The aromatic nitro compounds are produced, for instance, in thefollowing way.

First, the starting aromatic compound is dissolved or suspended in thehalogenated organic solvent as mentioned above at a temperature belowroom temperature (e.g. 10° to 30° C.), preferably under cooling with ice(at 0° to -30° C. for instance). Then a gaseous nitrogen oxide andozone-containing oxygen or air obtained by passing oxygen or air througha silent discharge tube are blown into the thus formed solution orsuspension under stirring. Ozone-containing oxygen or air is preferablyblown into said solution or suspension in the form of fine bubbles byusing, for example, sintered glass balls. The amounts of the nitrogenoxide and ozone-containing oxygen or air to be introduced is notspecifically restricted. Such amounts are properly adjusted according tothe produced amount of the desired aromatic nitro compound by analyzingthe reaction solution by gas chromatography. For instance, in the caseof mononitration, the amounts to be introduced are so selected that theywill be one molar equivalent or more to the aromatic compound, and inthe case of dinitration, the amounts are selected so that they will be 2molar equivalents or more to the aromatic compound. In case formation ofmany isomers is expected, the introduction of the gas may bediscontinued when one equivalent or less of the gas is introduced toterminate the reaction with a part of the starting aromatic compoundbeing left unreacted. The flow of the nitrogen oxide andozone-containing oxygen or air are also adjusted to be in an appropriaterange based on the produced amount of the desired aromatic nitrocompound by analyzing the reaction solution by gas chromatography.

The reaction temperature is usually room temperature or below, but incase the starting material used is of low reactivity, the reaction ispreferably carried out under moderate heating (for example at 40° to 50°C.). The reaction time is decided by analyzing the amount of theobjective substance (the aromatic nitro compound) in the reactionmixture by, for instance, gas chromatography. For obtaining a polynitrocompound according to the conventional methods, heating is generallyrequired, but according to the process of the present invention, it ispossible to accomplish polynitration by elongation of the reaction time(gas blowing time). Polynitration according to the process of thepresent invention is preferably applied to the aromatic compounds havingaromatic rings with high reactivity.

The reaction may be accomplished either according to an ordinary batchprocess or according to a continuous process in which the nitrogen oxideand ozone-containing oxygen or air are blown into a first reactor of aplural of reactors and the excess gas released from the first reactor isled into a second reactor, and so forth. In this way, the nitrogen oxideis perfectly consumed.

Further, in the process of the present invention, a solid phase carriersuch as molecular sieves, a cation exchange resin such as fluorine ionexchange resin, and a Lewis acid such as boron trifluoride etherate,silver oxide, methanesulfonic acid or the like may be added into thereaction system as a catalyst. The catalyst is usually added in anamount of 0.1 to 20 mol % based on the starting aromatic compound(reaction substrate). Additive property can be expected in the combineduse of the catalysts.

After the reaction is completed, the solvent is removed from thereaction mixture by distillation, filtration or other means, ifnecessary after neutralizing the reaction mixture, and the residue issubjected to an ordinary treatment such as fractional distillation,recrystallization, etc. to obtain the objective substance (the aromaticnitro compound) in a good yield. Purity of the objective substance canbe determined by gas chromatography. The used solvent may be recycledafter removing the by-product nitric acid and the remaining nitrogenoxide.

The process of the present invention has the advantages that consumptionof heat is small because of low reaction temperature, and that thereaction conditions are easily set according to the type of the startingmaterial to be nitrated and the type of the reaction to be performed(mononitration or polynitration) since the ozone concentration can beeasily adjusted by changing the silent discharge voltage of the ozonegenerator. The process of the present invention also has the advantagethat the solvent used in the reaction can be reused after removing theby-product nitric acid or the remaining nitrogen oxide by washing with asodium carbonate aqueous solution containing urea or by passing througha sodium carbonate powder layer.

BRIEF DESCRIPTION OF DRAWING

FIG. 1 is a diagram illustrating an example of the process for obtainingthe aromatic nitro compound from the aromatic compound through nitrationby the actions of the nitrogen oxide, ozone and a catalyst, andrecycling of the solvent and utilization of the by-product.

BEST MODE FOR CARRYING OUT THE INVENTION

The process of the present invention will be illustrated moreparticularly with reference to the examples thereof.

EXAMPLES 1-3

In 30 ml of dried dichloromethane was dissolved 5 ml of toluene, and thesolution was put into a pyrex three-necked flask and cooled to -10° C.Then nitrogen dioxide gas was introduced into the solution from an inletwhile introducing ozone-containing oxygen from another inlet, therebycarrying out the reaction for 3 hours. After the reaction, the nitrogenoxide existing dissolved in the reaction mixture was removed by passingair through the reaction mixture, then the reaction mixture was washedwith a sodium carbonate aqueous solution and the solvent was removed toobtain nitrotoluenes. The yield of the obtained mononitrotoluene and thecomposition of the isomers were as shown below. In Examples 2 and 3, thereaction was conducted by adding into the reaction system molecularsieves 4A or boron trifluoride etherate, respectively, followed by thesame post-treatments as described above.

    ______________________________________                                                   Composition of Isomers (%)                                         Catalyst     Ortho    Meta     Para  Yield (%)                                ______________________________________                                        Ex. 1                                                                              None        57.0     2.4    40.0  57                                     Ex. 2                                                                              Molecular   57.3     3.0    39.7  76                                          sieves 4A                                                                Ex. 3                                                                              Boron trifluor-                                                                           57.4     3.1    39.5  78                                          ide etherate                                                             ______________________________________                                    

EXAMPLE 4

In 50 ml of dichloromethane was dissolved 5 g of p-nitrotoluene and thesolution was cooled to 31 10° C. (using a pyrex three-necked flask).Thereafter, there were performed the same operations as in Example 1 toobtain 2,4-dinitrotoluene in a yield above 90%.

EXAMPLE 5

In 50 ml of dichloromethane was dissolved 5 g of benzene and thesolution was put into a pyrex three-necked flask and cooled to -10° C.Then nitrogen dioxide gas was introduced into the solution from an inletwhile ozone-containing oxygen was introduced from another inlet to carryout the reaction for 3 hours. After the reaction, the nitrogen oxideexisting dissolved in the reaction mixture was removed by passing airthrough the reaction mixture, then the reaction mixture was washed witha sodium carbonate aqueous solution and the solvent was removed toobtain a mixture of benzene, nitrobenzene and dinitrobenzene. The yieldof the obtained crude product and the composition of the isomers are asshown below.

    ______________________________________                                        Yield                81.0%                                                    ______________________________________                                        Composition (%)                                                               ______________________________________                                        Unreacted compound                                                                              50.0                                                        Nitrobenzene      46.5                                                        m-dinitrobenzene  2.3                                                         p-dinitrobenzene  1.1                                                         o-dinitrobenzene  ≦0.1                                                 ______________________________________                                    

EXAMPLE 6

Into a pyrex three-necked flask were placed 30 ml of dichloromethane, 5ml of toluene and 75 mg of silver oxide and the mixture was subjected tothe same treatments as in Example 1 to obtain 7.2 g of a crude product.The composition of the crude product determined by gas chromatography isshown below.

    ______________________________________                                        Yield                99.6%                                                    ______________________________________                                        Composition (%)                                                               ______________________________________                                        Unreacted compound 0.4                                                        o-nitrotoluene     55.2                                                       m-nitrotoluene     3.3                                                        p-nitrotoluene     41.5                                                       Dinitrotoluene     --                                                         ______________________________________                                    

EXAMPLE 7

In 50 ml of dichloromethane was dissolved 5 g of chlorobenzene and thesolution was put into a pyrex three-necked flask and cooled to -10° C.Then nitrogen dioxide was introduced into the solution from an inletwhile ozone-containing oxygen was introduced from another inlet to carryout the reaction for 3 hours. The resulting reaction mixture wassubjected to the same treatments as in Example 1 to obtainchloronitrobenzenes.

    ______________________________________                                        Yield                61.2%                                                    ______________________________________                                        Composition (%)                                                               ______________________________________                                        o-chloronitrobenzene                                                                             46.1                                                       m-chloronitrobenzene                                                                             1.1                                                        p-chloronitrobenzene                                                                             52.8                                                       ______________________________________                                    

EXAMPLE 8

To 50 ml of dried dichloromethane was added 5 g of benzoic acid and themixture was cooled to -10° C. (using a pyrex three-necked flask).Nitrogen dioxide gas was introduced into the mixture from an inlet whileozone-containing oxygen was introduced from another inlet to carry outthe reaction for 3 hours. After the reaction, the nitrogen oxideexisting dissolved in the reaction mixture was removed by passing airthrough the reaction mixture and the solvent was distilled away. To theresidue was added 20 ml of methanol and the solution was refluxed for 4hours to convert the product to methyl esters. Then the solvent wasremoved to obtain 7 g of the crude product. Yield was 95%.

Gas chromatographic analysis of the product showed the followingcomposition.

    ______________________________________                                        Composition (%)                                                               ______________________________________                                        Methyl benzoate    7.8                                                        Methyl o-nitrobenzoate                                                                           6.1                                                        Methyl p-nitrobenzoate                                                                           1.8                                                        Methyl m-nitrobenzoate                                                                           84.3                                                       ______________________________________                                    

EXAMPLE 9

In 50 ml of dry dichloromethane was suspended 0.5 g of anthraquinone andthe suspension was cooled to -10° C. (using a pyrex three-necked flask).To the suspension was added to 50 mg (20 mol %) of methanesulfonic acid,and then nitrogen dioxide gas was introduced into the suspension from aninlet while ozone-containing oxygen was introduced from another inletfor a period of 3 hours to carry out the reaction. Thereafter, thenitrogen oxide existing dissolved in the reaction mixture was removed bypassing air through the reaction mixture and then the solvent wasremoved to obtain 0.58 g of a crude nitro compounds (yield: 95%).

Gas chromatographic analysis of the product showed the followingcomposition.

    ______________________________________                                        Composition (%)                                                               ______________________________________                                        Anthraquinone (unreacted compound)                                                                   14.9                                                   β-nitroanthraquinone                                                                            8.8                                                    α-nitroanthraquinone                                                                           76.2                                                   ______________________________________                                    

This crude product was purified by column chromatography to obtain pureα-nitroanthraquinone.

EXAMPLE 10

In a pyrex three-necked flask was paced 50 ml of dry dichloromethane.Then 0.5 g of α-nitronaphthalene was added thereinto and the mixture wascooled to -10° C. Nitrogen dioxide was blown into the mixture from aninlet while ozone-containing oxygen was blown from another inlet for aperiod of 3 hours. After completion of the reaction, air was blown intothe reaction mixture to drive out the excess nitrogen dioxide. Then thesolvent was distilled away to obtain 0.6 g of crude dinitronaphthalenes(yield: 95%).

Gas chromatrographic analysis of the product showed the followingcomposition.

    ______________________________________                                        Composition (%)                                                               ______________________________________                                        1,5-dinitronaphthalene                                                                             21.7                                                     1,8-dinitronaphthalene                                                                             58.8                                                     Dinitronaphthalene   1.7                                                      other than 1,8- and 1,5-isomer                                                Trinitronaphthalene  18.3                                                     ______________________________________                                    

EXAMPLE 11

To 50 ml of chloroform was added 1.35 g of acetanilide, and the mixturewas placed into a pyrex three-necked flask and cooled to -10° C.Nitrogen dioxide was introduced into the mixture from an inlet whileintroducing ozone-containing oxygen from another inlet to carry out thereaction for 2.5 hours. The reaction mixture was subjected to the sametreatments as in Example 1 to obtain 1.6 g of nitroacetanilides. Gaschromatographic analysis of the product showed the followingcomposition.

    ______________________________________                                        Composition (%)                                                               ______________________________________                                        o-nitroacetanilide                                                                              80.1                                                        p-nitroacetanilide                                                                              12.9                                                        Dinitroacetanilides                                                                             7.0                                                         ______________________________________                                    

EXAMPLE 12

To 50 ml of chloroform was added 1.35 g of acetanilide, and the mixturewas placed into a pyrex three-necked flask and cooled to -10° C.Nitrogen dioxide was introduced into the mixture from an inlet whileintroducing ozone-containing oxygen from another inlet to carry out thereaction for 3 hours. The reaction mixture was subjected to the sametreatments as in Example 1 to obtain 2.2 g of nitroacetanilides. Gaschromatographic analysis of the product showed the followingcomposition.

    ______________________________________                                        Composition (%)                                                               ______________________________________                                        Mononitroacetanilides                                                                            0.6                                                        2,4-dinitroacetanilide                                                                           81.0                                                       2,6-dinitroacetanilide                                                                           18.4                                                       ______________________________________                                    

EXAMPLE 13

In 50 ml of dichloromethane was dissolved 5.0 g of each oft-butylbenzene, isopropylbenzene and ethylbenzene and each solution wasput into a three-necked flask and cooled to -10° C. Nitrogen dioxide wasintroduced into the solution from an inlet while ozone-containing oxygenwas introduced from another inlet to carry out the reaction for 3 hours.The reaction mixture was subjected to the same treatments as in Example1 to obtain the nitro compounds in the respective yields shown below.Gas chromatrographic (GC) analyses of the products showed the followingcompositions.

    ______________________________________                                                Starting material                                                                          Yield of product (g)                                     ______________________________________                                        (a)     t-butylbenzene                                                                             6.6                                                      (b)     Isopropylbenzene                                                                           6.5                                                      (c)     Ethylbenzene 5.6                                                      ______________________________________                                        Composition (%)                                                                       Results of GC analyses                                                Starting  o-nitro m-nitro    p-nitro                                          material  isomer  isomer     isomer                                                                              Others                                     ______________________________________                                        (a)       12.3    5.8        79.3  2.6                                        (b)       22.2    3.4        68.6  5.8                                        (c)       41.9    2.4        50.4  5.3                                        ______________________________________                                    

EXAMPLE 14

To 50 ml of dry dichloromethane was added 5.0 g of 5-t-butyl-3-xyleneand 500 mg of methanesulfonic acid and the mixture was put into athree-necked flask and cooled to 10° C. Nitrogen dioxide gas wasintroduced into the mixture from an inlet while ozone-containing oxygenwas introduced from another inlet to carry our the reaction for 3 hours.The reaction mixture was subjected to the same treatments as in Example1 to obtain 6.5 g of a product. Gas chromatographic analysis of theproduct showed the following composition.

    ______________________________________                                        Composition (%)                                                               ______________________________________                                        2-nitro-5-t-butyl-3-xylene                                                                        55.1                                                      4-nitro-5-t-butyl-3-xylene                                                                        12.9                                                      2,4-dinitro-5-t-butyl-3-xylene                                                                    15.6                                                      4,6-dinitro-5-t-butyl-3-xylene                                                                    5.5                                                       Others              10.9                                                      ______________________________________                                    

EXAMPLE 15

To 50 ml of dry dichloromethane was added 5.0 g of 5-t-butyl-3-xyleneand 500 mg of methanesulfonic acid, and the mixture was put into athree-necked flask and cooled to -10° C. Nitrogen dioxide gas wasintroduced into the mixture from an inlet while ozone-containing oxygenwas introduced from another inlet to carry out the reaction for 12hours. Air was blown into the reaction mixture to drive out the excessnitrogen dioxide and 7.3 g of crystals was isolated. This product wasfound to be 2,4,6- trinitro-5- t-butyl-3-xylene.

EXAMPLE 16

To 50 ml of dry dichloromethane were added 0.5 g of anthraquinone and 50mg of methyl disulfide, and the mixture was put into a three-neckedflask and cooled to 31 10° C. Nitrogen dioxide gas was introduced intothe mixture from an inlet while ozone-containing oxygen was introducedfrom another inlet to carry out the reaction for 12 hours. Then thenitrogen dioxide was removed in the same manner as in Example 9 and thesolvent was distilled away to obtain 0.55 g of crude nitro compounds.

Gas chromatographic analysis of the product showed the followingcomposition.

    ______________________________________                                        Composition (%)                                                               ______________________________________                                        Anthraquinone (unreacted compound)                                                                   trace                                                  2-nitroanthraquinone   5.4                                                    1-nitroanthraquinone   7.7                                                    1,8-dinitroanthraquinone                                                                             52.5                                                   1,5-dinitroanthraquinone                                                                             11.3                                                   1,6- or 1,7-dinitroanthraquinone                                                                     20.6                                                   2,6- or 2,7-dinitroanthraquinone                                                                     0.8                                                    ______________________________________                                    

INDUSTRIAL APPLICABILITY

According to the process of the present invention, the aromatic nitrocompounds, which are important as starting material for producing theorganic industrial products, can be produced under the mild conditionswithout using any mineral acid. Also, the process of this invention haslittle risk of causing pollution and is therefore favorable from theviewpoint of environmental protection.

We claim:
 1. A process for producing an aromatic nitro compound whichcomprises dissolving or suspending an aromatic compound in a halogenatedorganic solvent, and introducing into the resulting solution orsuspension a nitrogen oxide gas and ozone-containing oxygen or air,thereby subjecting the aromatic compound to nitration.
 2. The processaccording to claim 1, wherein the nitration is carried out in thepresence of a solid phase carrier, a cation exchange resin or a Lewisacid.
 3. The process of claim 2, wherein said aromatic compound isselected from the group consisting of benzene and its mononitro anddinitro compounds, toluene and its mononitro and dinitro compounds,o-xylene and its mononitro and dinitro compounds, m-xylene and itsmononitro and dinitro compounds, p-xylene and its mononitro and dinitrocompounds, benzene substituted by one or more alkyl groups having one ormore carbon atoms, and its mononitro and dinitro compounds, halogenatedbenzene and its mononitro and dinitro compounds, benzene substituted byan alkyl group and halogen, and its mononitro and dinitro compounds,benzene substituted by an alkoxy group and its mononitro and dinitrocompounds, naphthalene, anthracene, anthraquinone, pyrene andacetanilide optionally substituted with alkyl, alkoxy or halogen.
 4. Theprocess of claim 1, wherein said aromatic compound is selected from thegroup consisting of benzene and its mononitro and dinitro compounds,toluene and its mononitro and dinitro compounds, o-xylene and itsmononitro and dinitro compounds, m-xylene and its mononitro and dinitrocompounds, p-xylene and its mononitro and dinitro compounds, benzenesubstituted by one or more alkyl groups having one or more carbon atoms,and its mononitro and dinitro compounds, halogenated benzene and itsmononitro and dinitro compounds, benzene substituted by an alkyl groupand halogen, and its mononitro and dinitro compounds, benzenesubstituted by an alkoxy group and its mononitro and dinitro compounds,naphthalene, anthracene, anthraquionone, pyrene and acetanilideoptionally substituted with alkyl, alkoxy or halogen.